Fructose ketone derivatives, asymmetric olefin epoxidation

Previously, some fluorocyclohexanones were used in a catalytic amount with Oxone for asymmetric epoxidation reaction, but they gave a poor ee . It was found later that chiral ketones derived from fructose work well as asymmetric epoxidation catalysts and show high enantioselectivity in reactions of /rani-disubstituted and trisubsti-tuted olefins ". Cis and terminal olefins show low ee under these reaction conditions. Interestingly, the catalytic efficiency was enhanced dramatically upon raising the pH. Another asymmetric epoxidation was also reported using Oxone with keto bile acids. ... 

Subsequently, high chemoselectivity and enantioselectivity have been observed in the asymmetric epoxidation of a variety of conjugated enynes using fructose-derived chiral ketone as the catalyst and Oxone as the oxidant. Reported enantioselectivities range from 89% to 97%, and epoxidation occurs chemoselectively at the olefins. In contrast to certain isolated trisubstituted olefins, high enantioselectivity for trisubstituted enynes is noticeable. This may indicate that the alkyne group is beneficial for these substrates due to both electronic and steric effects. 

Tu Y, Wang ZX, Shi Y (1996) An efficient asymmetric epoxidation method for irans-olefins mediated by a fructose-derived ketone. J Am Chem Soc 118 9806... 

Tu, Y., Wang, Z.-X., Shi, Y. An Efficient Asymmetric Epoxidation Method fortrans-Olefins Mediated by a Fructose-Derived Ketone. J. Am. Chem. Soc. 1996,118, 9806-9807. 

In 1996, Shi made a huge development in this area, reporting the asymmetric epoxidation of alkenes using chiral dioxiranes generated in situ. The epoxidation works well for disubstituted tra s-olefins, and trisubstituted olefins using a fructose-derived ketone as a catalyst and oxone as an oxidant (Scheme 1.9) [26]. 

In 1996, Shi et al. [75] developed a fructose-derived ketone (Epoxone ) 183 as a highly effective asymmetric epoxidation catalyst. Shi s epoxidation is known to be the best for the asymmetric epoxidation of tramolefms and tri-substituted olefins. Shi s ketone is readily available and an efficient and selective oxidant that requires mild conditions. Ketone 183 could be synthesized [88] from inexpensive chiral starting material D-fructose, by ketalization and oxidation (Scheme 9.48). The enantiomer of 183 can be synthesized from L-fructose, which in turn could be obtained from commereially available L-sorbose. Chemists at DSM developed a scalable process for the preparation of Epoxone 183 in large quanities. 

In 2002, Shing et al. reported glucose-derived ketones 391 and 392. Ketone 391 epoxidizes tran -stilbene with up to 71% ee [277]. A series of L-arabinose-derived ketones 393-399 followed, and up to 90% ee was obtained for tran -stilbene epoxide with ketone 396 [278], In the same year, Zhao et al. reported three fructose-derived ketones and aldehydes 400-402 for the asymmetric epoxidation [279], Aldehyde 402 achieved 94% ee for tran -stilbene. hi 2009, Davis et al. presented a variety of conformationally restricted ketones 403, prepared from A-acetyl-D-glucosamine which show useful selectivities with terminal olefins (styrene 81% ee. Fig. 7.19) [280]. 

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